Organic semiconducting (OSC) materials are receiving growing interest mostly due to their rapid development in the recent years and the lucrative commercial prospects of organic electronics.
One particular area of importance is organic photovoltaics (OPV). Conjugated polymers have found use in OPVs as they allow devices to be manufactured by solution-processing techniques such as spin casting, dip coating or ink jet printing. Solution processing can be carried out cheaper and on a larger scale compared to the evaporative techniques used to make inorganic thin film devices. Currently, polymer based photovoltaic devices are achieving efficiencies above 8%.
In order to obtain ideal solution-processible OSC molecules two basic features are essential, firstly a rigid π-conjugated core unit to form the backbone, and secondly a suitable functionality attached to the aromatic core unit in the OSC backbone. The former extends π-π overlaps, defines the primary energy levels of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), enables both charge injection and transport, and facilitates optical absorption. The latter further fine-tunes the energy levels and enables solubility and hence processability of the materials as well as π-π interactions of the molecular backbones in the solid state.
A high degree of molecular planarity reduces the energetic disorder of OSC backbones and accordingly enhances charge carrier mobilities. Linearly fusing aromatic rings is an efficient way of achieving maximum planarity with extended π-π conjugation of OSC molecules. Accordingly, most of the known polymeric OSCs with high charge carrier mobilities are generally composed of fused ring aromatic systems and are semicrystalline in their solid states. On the other hand, such fused aromatic ring systems are often difficult to synthesize, and do also often show poor solubility in organic solvents, which renders their processing as thin films for use in OE devices more difficult. Also, the OSC materials disclosed in prior art still leave room for further improvement regarding their electronic properties.
Thus there is still a need for organic semiconducting (OSC) polymers which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processibility, especially a high solubility in organic solvents, and high stability in air. Especially for use in OPV cells, there is a need for OSC materials having a low bandgap, which enable improved light harvesting by the photoactive layer and can lead to higher cell efficiencies, compared to the polymers from prior art.
It was an aim of the present invention to provide compounds for use as organic semiconducting materials that are easy to synthesize, especially by methods suitable for mass production, and do especially show good processibility, high stability, good solubility in organic solvents, high charge carrier mobility, and a low bandgap. Another aim of the invention was to extend the pool of OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of the present invention have found that one or more of the above aims can be achieved by providing conjugated polymers as disclosed and claimed hereinafter. These polymers comprise one or more benzodithiophene based polycyclic units, or derivatives thereof, as represented by the following formulae, which are either tetrasubstituted or dialkylidene-substituted at the cyclopentadiene rings, and where A1 and A2 represent mono- or bicyclic aromatic or heteroaromatic rings, optionally together with further aromatic co-units.

Surprisingly it was found that these enlarged fused ring systems, and the polymers containing them, still show sufficient solubility in organic solvents, by introduction of alkyl or alkylidene substituents. Both the homo- and co-polymers can be prepared through known transition metal catalysed polycondensation reactions. As a result the polymers of the present invention were found to be attractive candidates for solution processable organic semiconductors both for use in transistor applications and photovoltaic applications. By further variation of the substituents on the fused aromatic ring system, the solubility and electronic properties of the monomers and polymers can be further optimised.
Conjugated polymers as disclosed in the present invention and as claimed hereinafter have not been reported in prior art so far.
WO 2010/027106 A1, EP 2 341 051 A1 and US 2011/166362 A1 disclose small molecules containing linearly fused polycyclic aromatic backbones as in structure (III) below, where one of W, X, Y and Z has to be a substituted amino group (NR), but does not disclose polymerizable monomers or polymers containing such a structural unit, and does neither disclose nor suggest polymers as claimed in the present invention.

C.-H. Wang, R.-R. Hu, S. Liang, J.-H. Chen, Z. Yang, J. Pei, Tet. Lett., 2005, 46, 8153 discloses benzodithiophene based polycyclic small molecules of structure (IV) as shown below (wherein R′ are alkoxy groups and R are aryl or spiro-connected aryl groups), but does not disclose polymerizable monomers or polymers containing such a structural unit, and does neither disclose nor suggest polymers as claimed in the present invention.
